There are two customary ways of embodying the rim of such mounted assemblies. These rims are either drop-centre rims with tapered bead seats inclined with respect to the axis of rotation of the assembly by an angle of 5° or 15°, or flat base rims or almost-flat base rims with seats inclined either at 0° or at 5° with respect to the axis of rotation.
Rims known as flat base rims have a mounting well the diameter of which is markedly less than the nominal diameter of the rim. This inside diameter of the rim may be considered by users to be too small because it does not, for example, make it possible to select brake drums of dimensions suited to effective braking of vehicles that are becoming increasingly powerful in relation to their weight.
As a result, these rims are commonly used for mounted assemblies intended for vehicles of the passenger vehicle and/or heavy goods vehicle type, but are used far less, if at all, for other types of vehicle such as, for example, site plant and civil engineering works vehicles.
To create a mounted assembly, particularly one of the “tubeless” type, a flat base rim needs there to be at least one removable lateral ring, one locking ring and a seal, and obviously the flat base rim that has a fixed flange on the opposite side to the side on which the parts are removable. Indeed the dimensions of the wheels of the vehicles and those of the tires, particularly the stiffness of the bottom regions, means that the said wheels have to be produced in several parts so that the tire can be mounted on a rim. At least three parts are therefore needed. In most cases though, the number of parts needed is greater than three and may sometimes be as much as six parts for large sizes of tires, not to mention the parts needed to fix the wheels to the vehicle. With the exception of the seals which are made of rubber, the parts of a rim are made of metal, and are therefore heavy, bulky and difficult to handle. It then follows that fitting and removing large and very large tires are difficult and lengthy operations. Fitting and/or removing a wheel equipped with such a tire requires the vehicle or the plant to be taken out of action for a not insignificant length of time which is therefore to the detriment of the productivity desired in the use of these vehicles.
Patent Application WO 00/71365 describes a technique for simplifying the fitting of tires, these being mounted directly on the hub, which then acts as a rim. Independent mounting rings then act as rim seats and are held in place by blocking rings which are secured to the hub notably using complementary profiles. With this technique, the locking ring is made up of a vulcanized rubber compound reinforced with and coating a reinforcing ring that is circumferentially elastic and radially resistant to compression.
A technique such as this is highly attractive because it makes it possible to eliminate the phases of mounting on a rim and fixing of a wheel to the vehicle, the tires being mounted directly on the hub via the mounting rings and locking rings. Furthermore, because the number of parts is greatly reduced, the phases of handling these elements are simpler.
However, whether using this latter technique or whether the tires are associated with wheels made up of several parts, when it is necessary to change a tire or to swap two tires around on the vehicle, a step of removing the wheel and/or the tire is always required; this involves deflating the tire, something which is indispensable for changing a tire, and practically indispensable, at least in part, when swapping mounted assemblies around, in order to reduce weight.
The time taken to deflate a 59/80R63 tire fitted to a vehicle of the dumper type is longer than thirty minutes, which means that, in order to swap around all the tires on the vehicle, a combined deflation time of at least two hours is needed.
Given that in a mine, a work cycle corresponding to the transportation of a full dumper body by a vehicle of the dumper type is usually shorter than this 30-minute time, it is clearly evident that the time spent working on the tires has a direct and significant influence on the productivity of the vehicles.
There is therefore in particular a desire to reduce the time taken to deflate such tires.
Tires for civil engineering works vehicles, such as the vehicles used in mines, for example of the dumper type, are usually inflated to a pressure of between 4 and 10 bar for customary loads and sizes.
The current deflation techniques involve freeing the internal part of the inflation valve in order to allow the air to escape. Shortening the deflation time could involve increasing the dimension of the current inflation valve systems, but their design would then become problematic and the flow rates caused by the pressures and the volume of air in this type of tire would endanger the operator who has to free the internal part of the valve.
Existing valves of the butterfly, spool or check valve type, of suitable sizes have been envisaged, but they present various disadvantages. On the one hand, they are too bulky to be installed on certain vehicles and, on the other hand, the maintenance of these valves requires full disassembly. Maintenance has to be taken into consideration because as the air escapes from the mounted assembly, it carries with it particles such as residues of corrosion coming from the wheel, fragments of tire, if the latter is deteriorating, and also liquids resulting from condensation and from the specific products intended to combat corrosion.
In the course of their studies and in particular when looking into creating the mounted assembly comprising large-sized tires, particularly tires the axial width of which is in excess of 18 inches, intended to be fitted to vehicles of the dumper type, increases in the productivity of which are endlessly being desired, the inventors thus set themselves an object of improving the times taken to deflate the tires.